Monthly Gridded Rainfall Files
Resolution: 0.25 x 0.25 degrees
Orientation: The gridded values are stored from west to east and from south
to north. For TMI the first value corresponds to 0.125E,
39.875S and the 1440th value to 359.875E, 39.875S.
File Sizes:
TRMM TMI -> 1440 x 320 x 8 x 2 (0-360E, 40N-40S, 8 fields)
SSM/I -> 1440 x 560 x 8 x 2 (0-360E, 70N-70S, 8 fields)
AMSR-E -> 1440 x 560 x 8 x 2 (0-360E, 70N-70S, 8 fields)
Each binary data file contains 8 data fields. The data is stored as 1-byte
values to avoid machine dependent issues (i.e. byte swapping). As a result,
the mean rainfall rate for the day is broken into its integer and
fractional parts. In addition, the total number of pixels and the number of
raining pixels are also stored using two bytes as described below. A full
description of the 8 data fields follows:
1) Integer rain rate in mm/hour (rain rate is truncated to nearest
integer value)
2) Fractional rain rate in mm/hour (fractional part of the rain rate is
multiplied by 100 and stored as an integer)
3) Percent convective rainfall (stored as an integer between 0 and 100)
4) Total number of valid pixels in 0.25 x 0.25 degree grid box (x10)
5) Total number of valid pixels in 0.25 x 0.25 degree grid box (remainder)
NPIX_total = 10 * B(4) + B(5)
6) Total number of raining pixels in 0.25 x 0.25 degreee grid box (x10)
7) Total number of raining pixels in 0.25 x 0.25 degreee grid box (remainder)
NPIX_raining = 10 * B(6) + B(7)
8) Flag (composed of two flags indicating surface type and rain flag)
The surface type flag is multiplied by 10 and added to the rain flag
Surface flag values:
0: Ocean
1: Land
2: Coast
3: Ice/other
Rain Flag values:
0: Grid box contains only valid pixels
1: Grid box contains ambiguous pixels
2: Grid box contains missing/unable to retrieve pixels
3: Grid box contains both ambiguous and missing pixels
4: Grid box is considered missing (i.e. no rain rate estimate available)
Examples:
0: Rain possible over ocean
10: Rain possible over land
21: Contains ambiguous rain over coast
32: Contains missing pixels over ice/other
Note: The monthly rain rate is computed based only on the valid pixels.
Ambiguous and/or missing pixels are not included. In addition, if the
number of days with ambiguous pixels is greater than 5 or the number
of days with missing pixels is greater than 5, the rain rate is set
to zero.